Ammonium zirconium carbonate solutions containing 10% by weight zirconia are commercially available and may be used whenever soluble zirconium in an alkaline environment is required. The solutions are commonly prepared by dissolving, at ambient temperatures, zirconium basic carbonate in a solution containing 3 moles of either commercial ammonium carbonate or a mixtue of ammonium bicarbonate and aqueous ammonia. From the method of preparation and the analysis of crystalline materials which have been obtained from these solutions the composition of the principal species present in the solution is believed to be (NH.sub.4) .sub.3 ZrOH (CO.sub.3).sub.3 which crystallises as a dihydrate.
Such ammonium zirconium carbonate solutions are extensively used for insolubilising the starch binders used in paper coating formulations. However, their use as starch insolubilisers and for other purposes is restricted because the solutions hydrolyse irreversibly at temperatures above 40.degree. to produce zirconia gels. Further, because the solutions are dilute, the major part of their cost of transportation is the cost of transporting water.
As disclosed in our co-pending patent application U.S. Pat. No. 3,810,852 although some zirconium compounds have been found to impart thixotropy to certain dispersions of polymer or copolymers, for example emulsion paints, the commerically available ammonium zirconium carbonate solutions have not been found effective for that purpose.
It has been found that concentrated ammonium and potassium zirconium carbonate solutions which are capable of imparting thixotropic properties to aqueous dispersions of polymers and copolymers are more resistant to hydrolysis at elevated temperatures than the more dilute solutions which are presently available and can easily be prepared. In these preparations only limited quantities, generally of the order of one instead of three moles, of added carbonate may be used, which is found to be advantageous both economically and in giving solutions which behave as emulsion paint polymer gellants.